Embodiments of the present invention relate to a chemical mechanical polisher having a heater and related methods.
In the fabrication of integrated circuits, chemical-mechanical planarization (CMP) can be used to smoothen the surface of a substrate for subsequent processing. A typical CMP apparatus comprises a substrate carrier that oscillates and presses a substrate against a polishing pad to polish the substrate. Optionally, a polishing medium can be supplied to the pad, the polishing medium comprising, for example, a polishing liquid and abrasive particles. CMP can be used, for example, to planarize dielectric layers, deep or shallow trenches filled with polysilicon or silicon oxide, and metal-containing films. It is believed that CMP polishing typically occurs as a result of both chemical and mechanical effects with a chemically altered layer being repeatedly formed at, and polished away from, the surface of the substrate.
However, during the CMP process, the polishing pad gradually wears out over time as a number of substrates are polished. One type of polishing pad comprises a circular polishing disc containing small abrasive particles that mechanically abrade and polish the substrate. This polishing disc has a sticky back which adheres to the surface of a polishing platen. After some time, the polishing disc wears out, and is replaced. However, pad replacement can be time consuming because the worn out disc has to be peeled off the polishing platen, the adhesive residue cleaned, and a new disc installed.
Another polishing pad, the roller pad, comprises a polishing sheet that is rolled up in a cylinder to provide a continuous feed of polishing pad. The roller pad can be replaced without requiring peeling of the pad from the platen or cleaning adhesive from the platen. Further, since the roller pad has a total polishing surface that is many times larger than the disk pad, the roller pad generally does not require as frequent replacement as the disk pad. The roller polishing pad is stretched across a rectangular polishing platen and gradually advanced across the platen to provide the polishing surface for a substrate. The polishing sheet comprises a web of abrasive material that mechanically abrades the substrates. After a single or set number of substrates are processed, the roller pad is advanced an incremental amount to provide a portion of new and unused polishing surface to the substrate. As one example, after each substrate is processed, the roller pad can be advanced from 5 to 10 mm. After these incremental advances deplete the entire roll of polishing pad sheet, a new roll can be installed.
For the roller pad CMP system, in order to reduce costs associated with substrate polishing, it is desirable to reduce the incremental rate of advance of the polishing sheet to use a lesser amount of polishing sheet material to polish a batch of substrates. However, when the incremental advancing rate is reduced, the substrates take longer to polish and this increase in polishing time is not desirable. Also, in both types of polishing pads, the polishing rate obtainable with the pad surface decreases with use as polishing residue containing ground-off substrate material and broken slurry particles clog up the polishing surface of the pad. Other changes in the topographical nature of the polishing pad can also lead to a reduced removal rate. A glazed pad surface provides reduced polishing efficiency because the polishing pad becomes smooth and clogged with debris, or simply holds less polishing medium. This results in a longer polishing time per substrate and increased consumption of polishing medium. Further, as the polishing efficiency of the pad reduces, the polishing depth can also vary from one substrate to another in a batch. These variations in polishing time and polishing rate from one substrate to another, and the increased usage of polishing medium and pad, are undesirable.